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  <script>
    let num = 10  // 1. 全局变量
    console.log(num)
    function fn() {
      console.log(num)
    }
    fn()

    // 2. 局部变量
    function fun() {
      let str = 'pink'
    }
    console.log(str)  // 错误
  </script>
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